Japanese people are very modest. This modesty affects the way they use language. Even if someone speaks perfect English, the cultural differences may still make the language sound a little strange.
It is considered rude and cocky to brag. It is even considered rude to say a fact, something you know for sure. Even if they know it's true they will add a softening word like, "I think, maybe, probably" to admit that they might be in error.
I really enjoy this game and I think I'm pretty good at it. Whenever I say something I add, "I think" or "maybe." In Japan I often put myself down just to watch the other people stick up for me. For this, I'm considered to be a very nice person. For example, at the school where I teach English, we have to make handouts for the children to take home. They should teach something and be fun if possible.
The other day my boss said to me, "I hope you are saving all the handouts that you make."
I replied, "Yes I'm saving them even though I don't think they are worth saving."
My boss smiled approvingly at me and replied, "No, your homeworks are very good. I like your ideas."
"No they are bad," I replied. I wasn't about to let her have the last word.
Sometimes this politeness tendency strikes an American as very out of place. When I flew home in December there was a Japanese pilot who spoke pretty good English. He made his own in-flight announcement as we were over the Pacific Ocean.
"We are now cruising at 11,000 meters. We will arrive in Chicago at 9 am................maybe." I was somewhat started by his uncertainty. What was the other possibility, that we wouldn't land at all? We would be late? We would arrive in a different city? No one else seemed to notice so I settled back and smiled to myself.